I made a printout of the SkinDatas of the same model exported to BONES and exported to my JSON-serialized format in an effort to solve my weight problem (and, with a little luck, kill the UV issue as well with the same proverbial stone). The following image shows that there's nearly six times more weights and jointIndices in the BONES version. SkinData doesn't hold animation information, does it? And if it's not animation, what could explain this? Thanks in advance.

And is it possible that other engines, like Unity, have some kind of logic to redistribute the weights for models that use more than four? Yet another question: is it trivial to increase the number of joints per vertices, or would that be a massive undertaking?

And is it possible that other engines, like Unity, have some kind of logic to redistribute the weights for models that use more than four? Yet another question: is it trivial to increase the number of joints per vertices, or would that be a massive undertaking?

assuming exporter supports it, it should be modified in loader code (jME, ardor3d). but again I dont see any good benefit for that

We have for the same model, two very different vertex counts (triple the number of triangles in jpct versus the unique vertex count which is typically less than the number of triangles in any given model), while retaining the same number of triangles, between jpct and 3ds max. But when we create our SkinData, we use only the number of unique vertices. Now we're thinking that we should be using the number of vertices in jpct. Did that make sense to you and do you agree?

We have for the same model, two very different vertex counts (triple the number of triangles in jpct versus the unique vertex count which is typically less than the number of triangles in any given model), while retaining the same number of triangles, between jpct and 3ds max. But when we create our SkinData, we use only the number of unique vertices. Now we're thinking that we should be using the number of vertices in jpct. Did that make sense to you and do you agree?

what exactly is your pipeline?

if you are creating your skeletal data from scratch in code, and loading your model from 3ds format or similar, yes, you possibly need to use number of vertices instead of unique vertex count.